The father of a man killed in the 1989 Tiananmen square crackdown has hanged himself in protest after two decades of failed attempts to seek government redress, a support group said Monday.

The group, known as the Tiananmen Mothers, said 73-year-old Ya Weilin's body was found in an underground parking garage below his residential complex in Beijing. He was believed to have killed himself on Friday.

An obituary the group posted on its website said that according to Ya's family, he had carried a note that detailed his son's death and declared that he would die in protest because the issue had not been addressed for more than 20 years.

Beijing police did not immediately respond to a faxed request for comment.

Ya's death came about a week before the anniversary of the night of 3-4 June 1989, when the military crushed the student-led protests, possibly killing thousands of people.

Official silence has been maintained about the incident, with nothing written in school textbooks and public discussion virtually taboo.

The Tiananmen Mothers group routinely issues open letters urging the country's leaders to account for the deaths. They have for years called for a full investigation, compensation to victims' families and punishment of those responsible for the crackdown. Members say the government has never responded.

Ya's son, Ya Aiguo, was shot in the head by troops in Beijing, according to the online obituary. A testimony by his mother on the same site says that at the time the 22-year-old had been waiting to be assigned a job and had gone out shopping with his girlfriend on the evening he was killed.

His father killed himself out of despair and to protest at the government's refusal to address the grievances of the victims' relatives, said Zhang Xianling, who knew Ya and his wife from the support group.

"The government's cold-blooded behaviour has caused this tragic ending," said Zhang, whose 19-year-old son died during the crackdown.

"I hope this incident will make the government circumspect and that such a thing will not happen again," Zhang said. "In this, the government has a responsibility. It owes a life now."

The Chinese government has never fully disclosed what happened when the military crushed the weeks-long Tiananmen protests, which it branded a "counterrevolutionary riot", nor allowed an independent investigation into the events and the fatalities.